Simultaneous determination of trace levels of 10 quinolones in swine, chicken, and shrimp muscle tissues using HPLC with programmable fluorescence detection

Intrinsic Fluorescence Markers for Food Characteristics, Shelf Life, and Safety Estimation: Advanced Analytical Approach

Food is a complex matrix of proteins, fats, minerals, vitamins, and other components. Various analytical methods are currently used for food testing. However, most of the used methods require sample preprocessing and expensive chemicals. New analytical methods are needed for quick and economic measurement of food quality and safety. Fluorescence spectroscopy is a simple and quick method to measure food quality, without sample preprocessing. This technique has been developed for food samples due to the application of a front-face measuring setup. Fluorescent compounds-fluorophores in the food samples are highly sensitive to their environment. Information about molecular structure and changes in food samples is obtained by the measurement of excitation-emission matrices of the endogenous fluorophores and by applying multivariate chemometric tools. Synchronous fluorescence spectroscopy is an advantageous screening mode used in food analysis. The fluorescent markers in food are amino acids tryptophan and tyrosine; the structural proteins collagen and elastin; the enzymes and co-enzymes NADH and FAD; vitamins; lipids; porphyrins; and mycotoxins in certain food types. The review provides information on the principles of the fluorescence measurements of food samples and the advantages of this method over the others. An analysis of the fluorescence spectroscopy applications in screening the various food types is provided.

Multiresidue Determination of 26 Quinolones in Poultry Feathers Using UPLC-MS/MS and Their Application in Residue Monitoring

As a non-traditional sample matrix, feather samples can be used to effectively monitor antibiotic addition and organismal residue levels in poultry feeding. Therefore, an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to simultaneously determine the residue levels of 26 quinolones in poultry feathers. The feather samples were extracted by sonication with a 1% formic acid and acetonitrile mixture in a water bath at 50 °C for 30 min, purified by the adsorption of multiple matrix impurities, dried with nitrogen, redissolved, and analyzed by UPLC-MS/MS. The linearity, limit of detection (LOD), limit of quantification (LOQ), recovery and precision were calculated. The 26 antibiotics demonstrated good linearity in the linear range. The recoveries and coefficients of variation were 78.9-110% and <13.7% at standard spiked levels of 10, 100 and 200 μg/kg, respectively. The LOD and LOQ were 0.12-1.31 and 0.96-2.60 μg/kg, respectively. The method also successfully identified quinolone residues in 50 poultry feather samples. The results showed that quinolones can accumulate and stabilize for a certain period of time after transferring from the body to the feathers of poultry.

Physiological responses and phytoremediation capacity of floating and submerged aquatic macrophytes exposed to ciprofloxacin

Ciprofloxacin (Cipro) water contamination is a global concern, having reached disturbing concentrations and threatening the aquatic ecosystems. We investigated the physiological responses and Cipro-phytoremediation capacity of one floating (Salvinia molesta D.S. Mitchell) and one submerged (Egeria densa Planch.) species of aquatic macrophytes. The plants were exposed to increased concentrations of Cipro (0, 1, 10, and 100 µg.Cipro.L^-1) in artificially contaminated water for 96 and 168 h. Although the antibiotic affected the activities of mitochondrial electron transport chain enzymes, the resulting increases in H₂O₂ concentrations were not associated with oxidative damage or growth reductions, mainly due to the activation of antioxidant systems for both species. In addition to being tolerant to Cipro, after only 96 h, plants were able to reclaim more than 58% of that from the media. The phytoremediation capacity did not differ between the species, however, while S. molesta bioaccumulate, E. densa appears to metabolize Cipro in their tissues. Both macrophytes are indicated for Cipro-phytoremediation projects.

QSRR modeling of the chromatographic retention behavior of some quinolone and sulfonamide antibacterial agents using firefly algorithm coupled to support vector machine

Quinolone and sulfonamide are two classes of antibacterial agents with an opulent history of medicinal chemistry features that contribute to their bacterial spectrum, efficacy, pharmacokinetics, and adverse effect profiles. The urgent need for their use, combined with the escalating rate of their resistance, necessitates the development of suitable analytical methods that accelerate and facilitate their analysis. In this study, the advanced firefly algorithm (FFA) coupled with support vector regression (SVR) was used to select the most significant descriptors and to construct two quantitative structure-retention relationship (QSRR) models using a series of 11 selected quinolone and 13 sulfonamide drugs, respectively, to predict their retention behavior in HPLC. Precisely, the effect of the pH value and acetonitrile composition in the mobile phase on the retention behavior of quinolones and sulfonamides, respectively, were studied. The obtained QSRR models performed well in both internal and external validations, demonstrating their robustness and predictive ability. Y-randomization validation demonstrated that the obtained models did not result by statistical chance. Moreover, the obtained results shed the light on the molecular features that influence the retention behavior of these two classes under the current chromatographic conditions.

Applications of Fluorescence Spectroscopy, RGB- and MultiSpectral Imaging for Quality Determinations of White Meat: A Review

Fluorescence spectroscopy, color imaging and multispectral imaging (MSI) have emerged as effective analytical methods for the non-destructive detection of quality attributes of various white meat products such as fish, shrimp, chicken, duck and goose. Based on machine learning and convolutional neural network, these techniques can not only be used to determine the freshness and category of white meat through imaging and analysis, but can also be used to detect various harmful substances in meat products to prevent stale and spoiled meat from entering the market and causing harm to consumer health and even the ecosystem. The development of quality inspection systems based on such techniques to measure and classify white meat quality parameters will help improve the productivity and economic efficiency of the meat industry, as well as the health of consumers. Herein, a comprehensive review and discussion of the literature on fluorescence spectroscopy, color imaging and MSI is presented. The principles of these three techniques, the quality analysis models selected and the research results of non-destructive determinations of white meat quality over the last decade or so are analyzed and summarized. The review is conducted in this highly practical research field in order to provide information for future research directions. The conclusions detail how these efficient and convenient imaging and analytical techniques can be used for non-destructive quality evaluation of white meat in the laboratory and in industry.

Detection of Bacterial Pathogens and Antibiotic Residues in Chicken Meat: A Review

Detection of pathogenic microbes as well as antibiotic residues in food animals, especially in chicken, has become a matter of food security worldwide. The association of various pathogenic bacteria in different diseases and selective pressure induced by accumulated antibiotic residue to develop antibiotic resistance is also emerging as the threat to human health. These challenges have made the containment of pathogenic bacteria and early detection of antibiotic residue highly crucial for robust and precise detection. However, the traditional culture-based approaches are well-comprehended for identifying microbes. Nevertheless, because they are inadequate, time-consuming and laborious, these conventional methods are not predominantly used. Therefore, it has become essential to explore alternatives for the easy and robust detection of pathogenic microbes and antibiotic residue in the food source. Presently, different monitoring, as well as detection techniques like PCR-based, assay (nucleic acid)-based, enzyme-linked immunosorbent assays (ELISA)-based, aptamer-based, biosensor-based, matrix-assisted laser desorption/ionization-time of flight mass spectrometry-based and electronic nose-based methods, have been developed for detecting the presence of bacterial contaminants and antibiotic residues. The current review intends to summarize the different techniques and underline the potential of every method used for the detection of bacterial pathogens and antibiotic residue in chicken meat.

Immunoassays on thiol-ene synthetic paper generate a superior fluorescence signal

The fluorescence-based detection of biological complexes on solid substrates is widely used in microarrays and lateral flow tests. Here, we investigate thiol-ene micropillar scaffold sheets ("synthetic paper") as the solid substrate in such assays. Compared to state-of-the-art glass and nitrocellulose substrates, assays on synthetic paper provide a stronger fluorescence signal, similar or better reproducibility, lower limit of detection (LOD), and the possibility of working with lower immunoreagent concentrations. Using synthetic paper, we detected the antibiotic enrofloxacin in whole milk with a LOD of 1.64 nM, which is on par or better than the values obtained with other common tests, and much lower than the maximum level allowed by European Union regulations. The significance of these results lays in that they indicate that synthetically-derived microstructured substrate materials have the potential to improve the performance of diagnostic assays.

Enantioseparation and determination of flumequine enantiomers in multiple food matrices with chiral liquid chromatography coupled with tandem mass spectrometry

The present work firstly described the enantioseparation and determination of flumequine enantiomers in milk, yogurt, chicken, beef, egg, and honey samples by chiral liquid chromatography-tandem mass spectrometry. The enantioseparation was performed under reversed-phase conditions on a Chiralpak IC column at 20°C. The effects of chiral stationary phase, mobile phase components, and column temperature on the separation of flumequine enantiomers have been studied in detail. Target compounds were extracted from six different matrices with individual extraction procedure followed by cleanup using Cleanert C18 solid phase extraction cartridge. Good linearity (R² >0.9913) was obtained over the concentration range of 0.125 to 12.5 ng g^-1 for each enantiomer in matrix-matched standard calibration curves. The limits of detection and limits of quantification of two flumequine enantiomers were 0.015-0.024 and 0.045-0.063 ng g^-1 , respectively. The average recoveries of the targeted compounds varied from 82.3 to 110.5%, with relative standard deviation less than 11.7%. The method was successfully applied to the determination of flumequine enantiomers in multiple food matrices, providing a reliable method for evaluating the potential risk in animal productions.

Health Risk Assessment of Banned Veterinary Drugs and Quinolone Residues in Shrimp through Liquid Chromatography–Tandem Mass Spectrometry

The presence of antibiotic residues in seafood and their effect on public health constitute a matter of concern for consumers worldwide. Antibiotic residues can have adverse effects on both humans and animals, especially residues of banned veterinary drugs. In this study, we applied a validated method to analyze veterinary drug residues in shrimp, including the levels of banned chloramphenicol, malachite green, leucomalachite green, and four nitrofuran metabolites as well as thiamphenicol, florfenicol, and five quinolones, which have no recommended maximum residual levels in shrimp tissues in Taiwan. We collected 53 samples of whiteleg, grass, or giant river shrimp from Taiwanese aquafarms and production areas from July 2016 to December 2017. We found 0.31 ng/g of a chloramphenicol in one grass shrimp, 5.62 ng/g of enrofloxacin in one whiteleg shrimp, 1.52 ng/g of flumequine in one whiteleg shrimp, and 1.01 ng/g of flumequine in one giant river shrimp, indicating that 7.55% of the samples contained veterinary drug residues. We evaluated the health risk by deriving the estimated daily intake (EDI). The quinolone residue EDI was below 1.0% of the acceptable daily intake recommended by the United Nations Food and Agriculture Organization and World Health Organization. The risk was thus discovered to be negligible, indicating no immediate health risk associated with shrimp consumption. The present findings can serve as a reference regarding food safety and in monitoring of the veterinary drug residues present in aquatic organisms. Continual monitoring of residues in shrimp is critical for further assessment of possible effects on human health.

A rapid and reliable assay to determine flumequine, marbofloxacin, difloxacin, and sarafloxacin in commonly consumed meat by micellar liquid chromatography

BACKGROUND

Micellar liquid chromatography - fluorescence detection was used to determine the antibiotics flumequine, marbofloxacin, difloxacin, and sarafloxacin in porcine, bovine, poultry, ovine, caprine, rabbit, and equine meat, to verify compliance with EU Regulation 37/2010 with regard to the occurrence of veterinary drugs in food.

RESULTS

The analytes were isolated from the matrix by ultrasonication-assisted leaching in a micellar solution, and the supernatant was filtered and directly injected. The fluoroquinolones were resolved in < 19 min using a C18 column, with an isocratic mobile phase of 0.05 mol L^-1 sodium dodecyl sulfate - 8% 1-butanol - 0.5% triethylamine buffered at pH 3. The limits of quantification (0.01-0.05 mg kg^-1 ) were below the maximum residue limits (0.15-0.4 mg kg^-1 ). The method was validated by EU Commission Decision 2002/657/EC guidelines.

CONCLUSION

The method shows practical advantages such as simplicity, low cost, eco-friendliness, safety, and applicability for routine analysis, and is useful for surveillance programs. © 2018 Society of Chemical Industry.

Occurrence and risk assessment of fluoroquinolones and tetracyclines in cultured fish from a coastal region of northern China

Occurrence and levels of 11 fluoroquinolones (FQs) and four tetracyclines (TC) in 14 cultured fish species from a coastal city in the northern China were investigated. Five FQs (ofloxacin, enoxacin, ciprofloxacin, enrofloxacin, and sarafloxacin) and oxytetracycline were detected. Lower detection frequencies of antibiotics were observed in the marine fish. The concentrations of ΣFQs ranged from not detectable (nd) to 130 ng/g wet weight (ww) (median, 7.2 ng/g ww), and the concentration range of ΣTCs was nd to 200 ng/g ww (median, nd ng/g ww). The Chinese snakehead contained the highest concentrations of ΣFQs (130 ng/g ww) and the small yellow croaker accumulated the highest concentrations of ΣTCs (200 ng/g ww), respectively. Although the calculated estimated daily intakes (EDI) suggested that the consumption of these cultured fish from this region was not associated with significant human health risks, this study provides useful information that will be helpful in the appropriate antibiotic use in aquaculture. To our knowledge, this can be the first report on the occurrence and levels of antibiotics in cage-cultured marine fish from the Bohai Rim region, China.

Usage, residue, and human health risk of antibiotics in Chinese aquaculture: A review

Aquaculture is a booming industry in the world and China is the largest producer and exporter of aquatic products. To prevent and treat diseases occurred in aquaculture, antibiotics are widely applied. However, the information of antibiotics used in Chinese aquaculture is still limited. Based on peer-reviewed papers, documents, reports, and even farmer surveys, this review summarized antibiotics used in Chinese aquaculture. In 2014, more than 47.4 million tonnes of farmed aquatic products were produced in mainland China. The outputs in the east and south parts of China can reach as much as 600 times higher than those in the northwest areas, which is clearly separated by the "Hu Line" - a line that marks a striking difference in the distribution of population. A total of 20 antibiotics belonging to eight categories have been reported for use, mainly via oral administration. However, only 13 antibiotics have been authorized for application in Chinese aquaculture and 12 antibiotics used are not authorized. Totally, 234 cases on antibiotic residues in Chinese aquatic products were recorded, including 24 fish species, eight crustacean species, and four mollusk species. Thirty-two antibiotics have been detected in aquatic products; quinolones and sulfonamides were the dominated residual chemicals. For specific compound, ciprofloxacin, norfloxacin, and sulfisoxazole have the highest concentrations. Except for a few cases, all residual concentrations were lower than the maximum residue limits. Through the consumption of aquatic products tainted by antibiotics, humans may acquire adverse drug reactions or antibiotic-resistant bacteria. However, the risk of antimicrobial resistance in human body, when exposed to antibiotics at sub-inhibitory concentrations, has not been exhaustively considered in the risk assessment. In addition, a national comprehensive investigation on the amount of antibiotics used in Chinese aquaculture is still needed in future studies.

Fluoroquinolone antibiotics: an emerging class of environmental micropollutants

The aim of this review paper is to provide a comprehensive overview of different chemical and environmental aspects concerning fluoroquinolone antibiotics as emerging contaminants. A literature survey has been performed based on 204 papers from 1998 to mid-2013, resulting in a dataset consisting out of 4100 data points related to physical-chemical properties, environmental occurrence, removal efficiencies, and ecotoxicological data. In a first part, an overview is given on relevant physical-chemical parameters to better understand the behavior of fluoroquinolones during wastewater treatment and in the environment. Secondly, the route of these antibiotics after their application in both human and veterinary surroundings is discussed. Thirdly, the occurrence of fluoroquinolone residues is discussed for different environmental matrices. The final part of this review provides a tentative risk assessment of fluoroquinolone compounds and their transformation products in surface waters by means of hazard quotients. Overall, this review shows that fluoroquinolone antibiotics have a wide spread use and that their behavior during wastewater treatment is complex with an incomplete removal. As a result, it is observed that these biorecalcitrant compounds are present in different environmental matrices at potentially hazardous concentrations for the aquatic environment. The latter calls for actions on both the consumption as well as the wastewater treatment aspect to diminish the discharge of these biological active compounds.

Obesity in the United States - dysbiosis from exposure to low-dose antibiotics?

The rapid increase in obesity prevalence in the United States in the last 20 years is unprecedented and not well explained. Here, we explore a hypothesis that the obesity epidemic may be driven by population-wide chronic exposures to low-residue antibiotics that have increasingly entered the American food chain over the same time period. We propose this hypothesis based on two recent bodies of published reports – (1) those that provide evidence for the spread of antibiotics into the American food chain, and (2) those that examine the relationship between the gut microbiota and body physiology. The livestock use of antimicrobial agents has sharply increased in the US over the same 20-year period of the obesity epidemic, especially with the expansion of intensified livestock production, such as the concentrated animal feeding operations. Observational and experimental studies support the idea that changes in the intestinal microbiota exert a profound effect on body physiology. We propose that chronic exposures to low-residue antimicrobial drugs in food could disrupt the equilibrium state of intestinal microbiota and cause dysbiosis that can contribute to changes in body physiology. The obesity epidemic in the United States may be partly driven by the mass exposure of Americans to food containing low-residue antimicrobial agents. While this hypothesis cannot discount the impact of diet and other factors associated with obesity, we believe studies are warranted to consider this possible driver of the epidemic.

Laser diode thermal desorption mass spectrometry for the analysis of quinolone antibiotic residues in aquacultured seafood

RATIONALE

Veterinary drug residue analysis of meat and seafood products is an important part of national regulatory agency food safety programs to ensure that consumers are not exposed to potentially dangerous substances. Complex tissue matrices often require lengthy extraction and analysis procedures to identify improper animal drug treatment. Direct and rapid analysis mass spectrometry techniques have the potential to increase regulatory sample analysis speed by eliminating liquid chromatographic separation.

METHODS

Flumequine, oxolinic acid, and nalidixic acid were extracted from catfish, shrimp, and salmon using acidified acetonitrile. Extracts were concentrated, dried onto metal sample wells, then rapidly desorbed (6 s) with an infrared diode laser for analysis by laser diode thermal desorption atmospheric pressure chemical ionization with tandem mass spectrometry (LDTD-MS/MS). Analysis was conducted in selected reaction monitoring mode using piromidic acid as internal standard.

RESULTS

Six-point calibration curves for each compound in extracted matrix were linear with r(2) correlation greater than 0.99. The method was validated by analyzing 23 negative samples and 116 fortified samples at concentrations of 10, 20, 50, 100, and 600 ng/g. Average recoveries of fortified samples were greater than 77% with method detection levels ranging from 2 to 7 /g. Three product ion transitions were acquired per analyte to identify each residue.

CONCLUSIONS

A rapid method for quinolone analysis in fish muscle was developed using LDTD-MS/MS. The total analysis time was less than 30 s per sample; quinolone residues were detected below 10 ng/g and in most cases residue identity was confirmed. This represents the first application of LDTD to tissue extract analysis. Published 2012. This article is a US Government work and is in the public domain in the USA.

Residues of fluoroquinolones in marine aquaculture environment of the Pearl River Delta, South China

Concentrations and distributions of selected fluoroquinolones (norfloxacin, ciprofloxacin and enrofloxacin) in water, sediments and nine kinds of fish species collected from 6 sites in two marine aquaculture regions of the Pearl River Delta, China, were analyzed by using high-performance liquid chromatography with fluorescence detector (HPLC). The results showed that the concentrations of ciprofloxacin and enrofloxacin were below the limits of quantification (LOQ) in all water samples except for norfloxacin. Norfloxacin and ciprofloxacin concentrations ranged from 1.88 to 11.20 ng g(-1) dry wt, 0.76-2.42 ng g(-1) dry wt in sediments collected from the Dapeng'ao region (sites 1-3) and ranged from 2.31 to 4.75 ng g(-1) dry wt, 1.26-1.76 ng g(-1) dry wt in sediments collected from the Hailing Island region (sites 4-6), respectively. However, no enrofloxacin was found in all sediment samples. The three fluoroquinolones (FQs) were detected in all fish samples, and the concentrations were higher in liver tissues than those in muscle tissues. The levels of norfloxacin were higher than ciprofloxacin and enrofloxacin in both liver and muscle tissues. Among the nine marine fish species, Siganus fuscescens from Hailing Island had a significantly high level of norfloxacin in liver tissue (254.58 ng g(-1) wet wt), followed by Sparus macrocephalus (133.15 ng g(-1) wet wt) from Dapeng'ao, and the lowest value was Lutianus argentimaculatus (5.18 ng g(-1) wet wt) from Hailing Island. The obtained results of FQs in present study do not represent a risk to the human health in Guangdong coastal area, based on the maximum residue limits (MRLs) established by Chinese Government and the acceptable daily intake (ADI) recommended by the Food and Agriculture Organization and World Health Organization (FAO/WHO).

Development of an indirect competitive ELISA for simultaneous detection of enrofloxacin and ciprofloxacin

Modified 1-ethyl-3-(3-dimethylaminopropy) carbodiimide (EDC) method was employed to synthesize the artificial antigen of enrofloxacin (ENR), and New Zealand rabbits were used to produce anti-ENR polyclonal antibody (pAb). Based on the checkerboard titration, an indirect competitive enzyme-linked immunosorbent assay (ELISA) standard curve was established. This assay was sensitive and had a linear range from 0.6 to 148.0 μg/kg (R(2) = 0.9567), with the half maximal inhibitory concentration (IC(50)) and limit of detection (LOD) values of 9.4 μg/kg and 0.2 μg/kg, respectively. Of all the competitive analogues, the produced pAb exhibited a high cross-reactivity to ciprofloxacin (CIP) (87%), the main metabolite of ENR in tissues. After optimization, the matrix effects can be ignored using a 10-fold dilution in beef and 20-fold dilution in pork. The overall recoveries and coefficients of variation (CVs) were in the ranges of 86%-109% and 6.8%-13.1%, respectively. It can be concluded that the established ELISA method is suitable for simultaneous detection of ENR and CIP in animal tissues.

Investigation of antibiotics in mollusks from coastal waters in the Bohai Sea of China

This study focused on the presence and distribution of 22 antibiotics, including eight quinolones, nine sulfonamides and five macrolides in mollusks from the Bohai Sea of China. 190 samples of eleven species were collected in 2006, 2007 and 2009. Laboratory analyses revealed that antibiotics were widely distributed in the mollusks with quinolones as the major compounds with concentrations of 0.71~1575.10 μg/kg, which were up to two orders of magnitude higher than those of sulfonamides (0~76.75 μg/kg) and macrolides (0~36.21 μg/kg). The contents of quinolones and macrolides did not show significant changes from 2006, 2007 to 2009, while sulfonamides decreased significantly from 2006 to 2009. Compared with other sites, the city of Dalian was more polluted with quinolones, while Beidaihe was more contaminated with erythromycin and sulfapyridine. In addition, Mactra veneriformis and Meretrix merehjgntrix Linnaeus contained higher concentrations of quinolones and sulfamonomethoxine, while Mytilus edulis had higher levels of erythromycin and sulfapyridine.

Synthesis and Identification of Norfloxacin Artificial Antigen

A multiresidue immunoassay method for determination of Fluoroquinolones (FQs) residues has been developed. For this purpose, NHS ester technology was employed to synthesize the immunogen and coating antigen of Norfloxacin (NFLX). SDS-PAGE, UV-visible spectra and Infrared spectra identification showed that the artificial antigen was conjugated successfully. Based on the square matrix titration, an icELISA method was established. The dynamic range in assay buffer was from 0.038 to 112.8 ng/mL, with LOD and IC50 value of 0.02 ng/mL and 1.2 ng/mL, respectively. This assay showed a high cross-reactivity to Ciprofloxacin (86%), Enrofloxacin (75%), Difloxacin (63%), Sarafloxacin (57%) and Pefloxacin (33.8%). The chemical effects on assay performance showed that the physiological pH (7.4) in assay buffer pursued the maximum absorbance (Amax) and the most sensitive IC50 values. The results suggest the artificial antigen was synthesized successfully, and the established immunoassay could be used for simultaneous detecting of Norfloxacin, Ciprofloxacin, Enrofloxacin, Difloxacin, Sarafloxacin and Pefloxacin residues in animal-original food samples.

Ionic liquid-based homogeneous liquid-liquid microextraction for the determination of antibiotics in milk by high-performance liquid chromatography

Ionic liquid-based homogeneous liquid-liquid microextraction (IL-based HLLME) high-performance liquid chromatography was developed and applied to the extraction, separation and determination of some antibiotics in milk. The proteins and lipids were removed by adding salt and adjusting the pH value. The homogeneous extraction was applied to the improvement of recoveries for IL phase and analytes. The experimental parameters of the IL-based HLLME, including salt concentration in sample solution, pH value of sample solution, volume of [C(6)MIM][BF(4)], amount of ion-pairing agent (NH(4)PF(6)), and extraction time, were evaluated. The limits of detection for enoxacin, pefloxacin, norfloxacin, enrofloxacin, sulfamethoxazole and sulfadimethoxine were 15.8, 7.07, 5.13, 4.00, 7.79 and 8.33 μg L(-1), respectively. When the proposed method was applied to the analysis of milk samples the recoveries of the analytes ranged from 92.5 to 118.6% and relative standard deviations were lower than 7.00%.

Development of an enrofloxacin immunosensor based on label-free electrochemical impedance spectroscopy

Enrofloxacin is the most widespread antibiotic in the fluoroquinolone family. As such, the development of a rapid and sensitive method for the determination of trace amounts of enrofloxacin is an important issue in the health field. The interaction of the enrofloxacin antigen to a specific antibody (Ab) immobilized on an 11-mercapto-undecanoic acid-coated gold electrode was quantified by electrochemical impedance spectroscopy. Two equivalent circuits were separately used to interpret the obtained impedance spectra. These circuits included one resistor in series with one parallel circuit comprised of a resistor and a capacitor (1R//C), and one resistor in series with two parallel RC circuits (2R//C). The results indicate that the antigen-antibody reaction analyzed using the 1R//C circuit provided a more sensitive resistance increment against the enrofloxacin concentration than that of the 2R//C circuit. However, the 2R//C circuit provided a better fitting for impedance spectra, and therefore supplies more detailed results of the enrofloxacin-antibody interaction, causing the increase of electron transfer resistance selectively to the modified layer, and not the electrical double layer. The antibody-modified electrode allowed for analysis of the dynamic linear range of 1-1000 ng/ml enrofloxacin with a detection limit of 1 ng/ml. The reagentless and label-free impedimetric immunosensors provide a simple and sensitive detection method for the specific determination of enrofloxacin.

Developing and optimizing an immunoaffinity cleanup technique for determination of quinolones from chicken muscle

An immunoaffinity chromatographic method was developed using an antibody mediated immunosorbent to selectively extract and purify 10 quinolones (marbofloxacin, norfloxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, difloxacin, sarafloxacin, oxolinic acid, and flumequine) in chicken muscle followed by HPLC. The operating conditions of the immunoaffinity chromatography (IAC) column were optimized, and the IAC has been successfully used for the isolation and purification of 10 quinolones from chicken muscle tissue. The optimized immunoaffinity column sample cleanup procedure combined with HPLC coupling to fluorescence detection afforded low limits of detection (0.1 ng g(-1) for danfloxacin and 0.15 ng g(-1) for all other quinolones tested). The method was also applied to determine quinolone residues in commercial muscle samples.

Development of a lateral flow colloidal gold immunoassay strip for the rapid detection of enrofloxacin residues

A rapid immunochromatographic lateral flow test strip of competitive format has been developed using a gold-conjugated monoclonal antibody for the specific determination of enrofloxacin (ENR) residues in chicken muscles. For this purpose, a specific monoclonal antibody (mAb) for ENR was generated and characterized. The mAb showed negligible cross-reactivity with other related compounds. Using ENR standards prepared in chicken muscle extracts from 0 to 24.3 ng/mL (microg/kg), the method indicated that the detection limit of the test strip, as measured in a strip scanner, was as low as 0.138 microg/kg of ENR and the half-maximal inhibition concentration (IC(50)) was 0.935 microg/kg. For samples spiked at 10, 20, and 30 microg/kg, the recovery was between 85.3 and 96.1% and the coefficient of variation [CV (%)] was between 4.5 and 7.91%. Parallel analysis of muscle samples from chickens fed ENR showed good comparable results obtained from the test strip and LC-MS. Each test requires 5-10 min. The data indicate that the method has high sensitivity, specificity, and the advantages of simplicity and speed of performance. Therefore, the test strip provides a useful screening method for quantitative, semiquantitative, or qualitative detection of ENR residues in chicken muscles.

Determination of enrofloxacin and ciprofloxacin in milk using molecularly imprinted solid-phase extraction

A molecularly imprinted solid-phase extraction procedure was developed for the simultaneous identification of enrofloxacin and its active metabolite, ciprofloxacin, in milk samples. Water-compatible molecularly imprinted polymers synthesized in a water-methanol system show a high degree of cross-reactivity for enrofloxacin and ciprofloxacin in aqueous environments. The imprinted particles were applied as selective sorbents in a solid-phase extraction process focusing upon complex milk matrices, which allowed the matrix compounds present in milk samples to be removed effectively. The extracts were sufficiently clean for further chromatographic analysis, and no interference originating from the biological matrix was observed. The mean recoveries of enrofloxacin and ciprofloxacin from milk sample were 82.6-93.5% and 81.2-94.8%, respectively, with the RSD less than 7.5%. This method is simple and sensitive, and is therefore an alternative tool to the existing HPLC methods for analyzing residual enrofloxacin and ciprofloxacin in biological samples.